The present invention relates to a drying machine which comprises a storage chamber to store a matter to be dried and which executes a drying operation for the matter to be dried in the storage chamber.
In such a drying machine, an electric heater or a gas burning heater has heretofore been used as a heat source. After heating outside air by the electric heater or the burning heater to produce high-temperature air, the air is blown into a storage chamber in which the matter to be dried is stored to thereby dry the matter to be dried in the storage chamber. Moreover, the high-temperature air in the storage chamber, which has dried the matter to be dried, is discharged to the outside.
However, in the drying machine using such an electric heater or gas burning heater, as low-temperature humid air outside the storage chamber is used for the high-temperature air sent into the storage chamber, a long time is required until the matter to be dried dries. Therefore, an energy consumption amount to dry the matter to be dried is increased, leading to a problem of increased energy costs such as an electric bill and a gas bill.
To solve the problem, a clothing drying machine has been developed which is constituted of a compressor, a heating coil, an expansion valve, and a cooling coil. A heat pump capable of circulating a heat exchange medium is utilized. The matter to be dried is dried by the high-temperature air heated by the heating coil. Moisture evaporated from the matter to be dried is condensed by the cooling coil, and removed, and a condensed water content is discarded (see, e.g., Japanese Patent Application Laid-Open No. 11-99299).
On the other hand, the matter to be dried in the clothing drying machine includes clothing made of materials whose quality is easily changed by heat. Such a matter to be dried is easily damaged by hot air during the drying operation, and it is therefore necessary to lower temperature of the hot air discharged into the storage chamber during the drying operation. Thus, in the conventional clothing drying machine using the heat pump, it is conceivable to restrict an operation frequency of the compressor to lower temperature of a high-temperature high-pressure refrigerant of a gas cooler (radiator) which exchanges heat with the air supplied into the storage chamber. However, in such a case, a pressure increases on a low-pressure side due to a pressure drop caused on a high-pressure side of a refrigerant circuit configured in the heat pump, thus leading to an increase in a refrigerant evaporation temperature of an evaporator. This causes a problem that it is not possible to sufficiently cool down the air from the storage chamber which exchanges heat with the evaporator, and the moisture evaporated from the matter to be dried cannot be condensed and removed. Particularly, in a dry cleaner using a petroleum-based solvent as a cleaning fluid, there are problems that the solvent cannot be sufficiently recovered, that a rate of recovering the solvent decreases, and that a running cost is increased due to an increase in an amount of added solvent.